In Long Term Evolution (LTE) Release 8 (R8), a base station may configure a wireless transmit/receive unit (WTRU) with downlink (DL) and uplink (UL) resources on a single DL carrier and a single UL carrier, respectively. The pair of DL and UL carriers may be considered to form a cell of the wireless network. The WTRU may take certain actions in response to the configuration, configuration parameters and access issues related to the activation/deactivation process. In LTE R8, there is no ambiguity from the perspective of the WTRU in taking action since the DL and UL resources are associated with the single DL carrier and the single UL carrier, respectively, which form a serving cell of the WTRU. In multi-carrier wireless systems, the WTRU may be assigned multiple serving cells, each consisting of one DL component carrier and possibly also one UL component carrier (CC). The WTRU may need to act and respond differently if the WTRU may be configured with multiple serving cells.